If you're the type of leader who takes it personally when an employee quits, you're shooting yourself in the foot.

Sure, it's never ideal to lose talented people, but you should always set yourself up as a boss who employees want to return to work with in the future. If you respect their decision and make their exit comfortable, they might later give you a referral, provide free consulting, or even come back to your company. 

Michael Schrage, a research fellow at MIT Sloan School's Center for Digital Business, writes in Harvard Business Review about maximizing the all-important "Return on Ex-Employees." "Ironically, one of the most powerful and persuasive ways to inspire commitment inside the enterprise is maintaining healthy relationships with high achievers who've left the organization," Schrage writes. "Talented 'exes' should be seen as assets who can make the organization more valuable and an even better place to work."

Check out all the reasons you need to keep up relationships with ex-employees below.

1. A stream of referrals

If your culture is welcoming and supportive, you'll have ex-employees who will spread the gospel. Schrage says ex-employees are a potential gold mine of revenue and savings, citing the consulting firm McKinsey as a prime example. "Not incidentally, McKinsey maintains both a formal and extensive informal 'alumni network' of partners and associates," he writes. "The firm deliberately invests in its exes as assets, people, and part of a community."

2. A go-to reference

As they make their way into other companies and industries, your ex-employees will have access to talent pools that you don't. Don't throw away this potential resource. "When high-performance exes provide positive references and recommendations to top-tier job candidates, they pay their former employer an enormous compliment," Schrage says. 

3. A natural resource

Just because a talented person leaves your company, it doesn't mean they're unable to help you. If you respect their decision and support them, you can call on them when needed. You want an environment where ex-employees willfully act as a resource. If you need a consultant but can't pay, take an ex-employee out to lunch and pick their brain. "I was told by one company that this sort of informal sharing and advisory review goes on--respectfully--'all the time,'" Schrage writes.

4. Boomerang employees

A company culture that allows for employees to go out and explore opportunities is one where creative, talented and motivated folks will congregate--and in some cases, ultimately return to. "Some firms treat exes, especially the talents, as defectors and traitors who will never be allowed to return," Schrage says. "Firms that catch their boomerangs effectively ... signal that diversity of experience outside the firm can be a great thing."